Atomic layer deposition of metal oxide materials for memory applications

ABSTRACT

Embodiments of the invention generally relate to nonvolatile memory devices, such as a ReRAM cells, and methods for manufacturing such memory devices, which includes optimized, atomic layer deposition (ALD) processes for forming metal oxide film stacks. The metal oxide film stacks contain a metal oxide coupling layer disposed on a metal oxide host layer, each layer having different grain structures/sizes. The interface disposed between the metal oxide layers facilitates oxygen vacancy movement. In many examples, the interface is a misaligned grain interface containing numerous grain boundaries extending parallel to the electrode interfaces, in contrast to the grains in the bulk film extending perpendicular to the electrode interfaces. As a result, oxygen vacancies are trapped and released during switching without significant loss of vacancies. Therefore, the metal oxide film stacks have improved switching performance and reliability during memory cell applications compared to traditional hafnium oxide based stacks of previous memory cells.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 13/224,021, entitled“Atomic Layer Deposition of Metal Oxide Materials for MemoryApplications,” filed on Sep. 1, 2011, incorporated herein by referencein its entirety for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention generally relate to memory devices andmethods for manufacturing such memory devices.

2. Description of the Related Art

Nonvolatile memory elements are used in systems in which persistentstorage is required. For example, digital cameras use nonvolatile memorycards to store images and digital music players use nonvolatile memoryto store audio data. Nonvolatile memory is also used to persistentlystore data in computer environments. Nonvolatile memory is often formedusing electrically-erasable programmable read only memory (EPROM)technology. This type of nonvolatile memory contains floating gatetransistors that can be selectively programmed or erased by applicationof suitable voltages to their terminals.

As fabrication techniques improve, it is becoming possible to fabricatenonvolatile memory elements with increasingly smaller dimensions.However, as device dimensions shrink, scaling issues are posingchallenges for traditional nonvolatile memory technology. This has ledto the investigation of alternative nonvolatile memory technologies,including resistive switching nonvolatile memory.

Resistive switching nonvolatile memory is formed using memory elementsthat have two or more stable states with different resistances. Bistablememory has two stable states. A bistable memory element can be placed ina high resistance state or a low resistance state by application ofsuitable voltages or currents. Voltage pulses are typically used toswitch the memory element from one resistance state to the other.Nondestructive read operations can be performed to ascertain the valueof a data bit that is stored in a memory cell.

Resistive switching based on transition metal oxide switching elementsformed of metal oxide films has been demonstrated. Although metal oxidefilms such as these exhibit bistability, the resistance of these filmsand the ratio of the high-to-low resistance states are ofteninsufficient to be of use within a practical nonvolatile memory device.For instance, the resistance states of the metal oxide film shouldpreferably be significant as compared to that of the system (e.g., thememory device and associated circuitry) so that any change in theresistance state change is perceptible. The variation of the differencein resistive states is related to the resistance of the resistiveswitching layer. Therefore, a low resistance metal oxide film may notform a reliable nonvolatile memory device. For example, in a nonvolatilememory that has conductive lines formed of a relatively high resistancemetal such as tungsten, the resistance of the conductive lines mayoverwhelm the resistance of the metal oxide resistive switching element.Therefore, the state of the bistable metal oxide resistive switchingelement may be difficult or impossible to sense.

Similar issues can arise from integration of the resistive switchingmemory element with current steering elements, such as diodes and/orresistors. The resistance of the resistive switching memory element (atleast in its high resistance state) is preferably significant comparedto the resistance of the current steering elements, so that theunvarying resistance of the current steering element does not dominatethe resistance of the switching memory element, and thus reduce themeasurable difference between the “on” and “off” states of the formedmemory device (e.g., logic states of the device). However, since thepower that can be delivered to a circuit containing a series ofresistive switching memory elements and current steering elements istypically limited in most conventional nonvolatile memory devices (e.g.,CMOS driven devices), it is desirable to form each of the resistiveswitching memory elements and current steering elements in the circuitso that the voltage drop across each of these elements is small, andthus resistance of the series connected elements does not cause thecurrent to decrease to an undesirable level due to the fixed appliedvoltage (e.g., about 2-5 volts).

As nonvolatile memory device sizes shrink, it is important to reduce therequired currents and voltages that are necessary to reliably set, resetand/or determine the desired “on” and “off” states of the device tominimize resistive heating of the device and cross-talk between adjacentdevices. Moreover, in cases where multiple formed memory devices areinterconnected to each other and to other circuit elements it isdesirable to minimize the device performance variation between onedevice to the next to assure that the performance of the formed circuitperforms in a desirable manner.

The transition metal oxide materials used within the resistive switchingelements have been doped with highly reactive dopant metals which causeproblems to the bulk switching layer. Highly reactive dopant metals mayextract oxygen from the bulk switching layer and cause excessive leakagein the resistive switching element. Also, it is usually difficult tocontrol the removal of appreciable amount of oxygen from the metal oxidefilms. If the metal oxide film contains hafnium oxide, the loss of toomuch oxygen provides an excess hafnium metal which in turn may causedevice failure. The excess hafnium metal may chemical reduces siliconoxide material generally disposed between the bottom electrode and themetal oxide film and turn forms hafnium silicide—which has undesirableproperties at this interface.

Therefore, there is a need for an efficient and controllable process toform a metal oxide film stack for a nonvolatile memory device.

SUMMARY OF THE INVENTION

Embodiments of the invention generally relate to nonvolatile memorydevices and methods for manufacturing such memory devices. Embodimentsdescribed herein provide methods for forming improved memory devices,such as a ReRAM cells, and also provide optimized, atomic layerdeposition (ALD) processes for forming metal oxide film stacks. Themetal oxide film stacks described herein contain at least two metaloxide layers, such as a metal oxide coupling layer disposed on a metaloxide host layer. In some examples, the metal oxide film stacks maycontain an amorphous metal oxide coupling layer disposed on acrystalline metal oxide host layer—therefore—the crystalline metal oxidelayer has a grain boundary which adjoins the amorphous metal oxide layerat the interface therebetween. In other examples, each of the metaloxide layers contained within the metal oxide film stacks is crystallineand has a different grain structure and/or size from theother—therefore—these crystalline metal oxide layers have differentgrain boundaries adjoining at a misaligned grain interface therebetween.

The misaligned grain interface disposed between the two metal oxidelayers facilitates oxygen vacancy movement or filamentary formation. Themisaligned grain interface contains numerous grain boundaries thatextend parallel to the electrode interfaces, in contrast to the grainsin the bulk film that extend perpendicular to the electrode interfaces.As a result, oxygen vacancies are trapped and released during switchingwithout any overall loss or without significant loss of vacancies.Therefore, the metal oxide film stacks have improved switchingperformance and reliability during memory cell applications—compared toprevious memory cells which generally contain traditional hafnium oxidebased stacks.

The described ALD processes are techniques for depositing ultra-thinmetal oxide films due to practical advantages which includes simple andaccurate thickness control, precise control of dopant/elementconcentrations and distributions, excellent reproducibility anduniformity, and capability to produce conformal films at sharpinterfaces and trenches with high aspect ratio.

In one embodiment, a metal oxide film stack, disposed between upper andlower electrodes, contains a metal oxide coupling layer disposed on ametal oxide host layer and a grain boundary formed at the interface ofthe metal oxide host layer and the metal oxide coupling layer. In oneexample, a crystalline hafnium oxide layer may be formed by a first ALDprocess and an amorphous hafnium aluminate layer may be formed by asecond ALD process.

In another embodiment, the metal oxide film stack contains a crystallinemetal oxide coupling layer disposed on a crystalline metal oxide hostlayer such that the metal oxide layers have a misaligned grain interfaceformed therebetween. The crystalline metal oxide material of the hostlayer has an average grain size greater than the crystalline metal oxidematerial of the coupling layer.

In one embodiment described herein, a method for fabricating a resistiveswitching memory element, such as a memory device, is provided andincludes forming a metal oxide film stack over a lower electrodedisposed on a substrate, wherein the metal oxide film stack contains ametal oxide coupling layer disposed on a metal oxide host layer, and aninterface is formed between the metal oxide host layer and the metaloxide coupling layer. The interface facilitates oxygen vacancy betweenthe crystalline metal-rich oxide host material of the metal oxide hostlayer and the amorphous metal-rich oxide coupling material of the metaloxide coupling layer.

The method further provides forming the metal oxide film stack whichincludes depositing the metal oxide host layer over the lower electrodeduring a first ALD process, wherein the metal oxide host layersubstantially contains a crystalline metal-rich oxide host material. Thecrystalline metal-rich oxide host material may be represented by thegeneric chemical formula of MO_(x), where M is a metal selected fromhafnium, zirconium, or titanium and x may be within a range from about1.65 to about 1.95. The method also includes depositing the metal oxidecoupling layer over the metal oxide host layer during a second ALDprocess, wherein the metal oxide coupling layer may be a metal oxidelaminate and may substantially contain an amorphous metal-rich oxidecoupling material. The amorphous metal-rich oxide coupling material maybe represented by the generic chemical formula of MM′_(y)O_(z), where Mmay be the same type of metal selected for the crystalline metal-richoxide host material contained within the metal oxide host layer, M′ maybe a dopant metal selected from aluminum, yttrium, or lanthanum, y maybe within a range from about 0.05 to about 0.50, and z may be within arange from about 1.50 to about 2.50.

In some of the described examples, an amorphous hafnium aluminate layermay be deposited, formed, or otherwise disposed on or over a crystallinehafnium oxide layer. In one example, the crystalline metal-rich oxidehost material has the generic chemical formula of HfO_(x), where x maybe within a range from about 1.70 to about 1.90, and the amorphousmetal-rich oxide coupling material has the generic chemical formula ofHfAl_(y)O_(z), where y may be within a range from about 0.05 to about0.50, and z may be within a range from about 1.50 to about 2.50. In someexamples, the aluminum dopant is light or has a low concentration suchthat y may be within a range from about 0.05 to about 0.15 and z may bewithin a range from about 1.50 to about 2.10. In other examples, thealuminum dopant is heavy or has a high concentration such that y may bewithin a range from about 0.40 to about 0.50 and z may be within a rangefrom about 2.10 to about 2.50. In many examples, x may be within a rangefrom about 1.75 to about 1.85, for example, about 1.80.

The metal oxide host layer may have a thickness within a range fromabout 5 Å to about 100 Å, such as from about 10 Å to about 80 Å, such asfrom about 15 Å to about 50 Å, for example, about 30 Å. The metal oxidecoupling layer may have a thickness within a range from about 3 Å toabout 80 Å, such as from about 5 Å to about 50 Å, such as from about 5 Åto about 30 Å, for example, about 20 Å.

In one embodiment, the first ALD process includes sequentially providinga metal source gas and an oxidizing agent into a deposition chamberduring a metal-rich oxidizing ALD process. The metal source gas maycontain a tetrakis(dialkylamido) hafnium compound and the oxidizingagent may contain water during the metal-rich oxidizing ALD process. Insome examples, the tetrakis(dialkylamido)hafnium compound istetrakis(dimethylamido)hafnium. The second ALD process includessequentially providing a first metal source gas, a second metal sourcegas, and an oxidizing agent into the deposition chamber during ametal-rich oxidizing ALD process. The first metal source gas may containa tetrakis(dialkylamido) hafnium compound, the second metal source gasmay contain an alkyl aluminum compound, and the oxidizing agent maycontain water. In some examples, the tetrakis(dialkylamido)hafniumcompound is tetrakis(dimethylamido)hafnium and the alkyl aluminumcompound is trimethylaluminum.

In another embodiment, the first ALD process further includessequentially providing a first metal source gas, a purge gas, anoxidizing agent, and the purge gas into a deposition chamber whileforming the crystalline metal-rich oxide host material during a firstALD cycle during the first ALD process, and repeating the first ALDcycle while increasing the thickness of the metal oxide host layer untilthe thickness is within a range from about 5 Å to about 100 Å.Additionally, the second ALD process further includes sequentiallyproviding a second metal source gas, the purge gas, the first metalsource gas, the purge gas, the oxidizing agent, and the purge gas intothe deposition chamber while forming the amorphous metal-rich oxidecoupling material during a second ALD cycle during the second ALDprocess. Thereafter, the method includes repeating the second ALD cyclewhile increasing the thickness of the metal oxide coupling layer untilthe thickness is within a range from about 3 Å to about 80 Å. In someexamples the first metal source gas may contain a tetrakis(dialkylamido)hafnium compound, the second metal source gas may contain an alkylaluminum compound, the oxidizing agent may contain water, and the purgegas may contain argon, nitrogen, hydrogen, mixtures thereof, orcombinations thereof.

In another embodiment, the method further provides forming a siliconoxide layer over the lower electrode, and subsequently, forming themetal oxide host layer over the silicon oxide layer. The silicon oxidelayer may contain native silicon oxides or silicon dioxide. Generally,the silicon oxide layer has a thickness within a range from about 2 Å toabout 20 Å, a thickness within a range from about 2 Å to about 40 Å,such as from about 2 Å to about 20 Å, such as from about 5 Å to about 10Å.

In various other examples, the metal source gas may contain atetrakis(dialkylamido)zirconium compound, such astetrakis(dimethylamido)zirconium, or a tetrakis(dialkylamido)titaniumcompound, such as tetrakis(dimethylamido)titanium, and the oxidizingagent may contain water during the metal-rich oxidizing ALD process.

In another embodiment described herein, a method for fabricating aresistive switching memory element, such as a memory device, is providedand includes forming a metal oxide film stack over a lower electrodedisposed on a substrate, wherein the metal oxide film stack contains ametal oxide coupling layer disposed on a metal oxide host layer. Amisaligned grain interface is formed between the grain boundary of themetal oxide host layer and the grain boundary of the metal oxidecoupling layer. The misaligned grain interface facilitates oxygenvacancy between the metal-rich oxide host material and the metal-richoxide coupling material. The method further provides forming the metaloxide film stack which includes forming the metal oxide host layer overthe lower electrode during a first ALD process, wherein the metal oxidehost layer substantially contains a crystalline metal-rich oxide hostmaterial having the generic chemical formula of MO_(x), where M is ametal selected from hafnium, zirconium, or titanium and x may be withina range from about 1.65 to about 1.95.

The method further includes forming the metal oxide coupling layer overthe metal oxide host layer during a second ALD process, wherein themetal oxide coupling layer substantially contains a crystallinemetal-rich oxide coupling material having the generic chemical formulaof M′O_(y), where M′ is a metal selected from hafnium, zirconium, ortitanium, y may be within a range from about 1.65 to about 1.95, and anaverage grain size of the crystalline MO_(x) host material is greaterthan an average grain size of the crystalline M′O_(y) coupling material.

In many embodiments, a grain size ratio of the average grain size of thecrystalline MO_(x) host material to the average grain size of thecrystalline M′O_(y) coupling material is within a range from about 1.05to about 2.0. In some examples, the grain size ratio may be within arange from about 1.10 to about 1.50, for example, about 1.25. Theaverage grain size of the crystalline MO_(x) host material may be withina range from about 30 nm to about 40 nm, and the average grain size ofthe crystalline MO_(x) coupling material may be within a range fromabout 25 nm to about 35 nm.

In some examples, the crystalline metal-rich oxide host material has thegeneric chemical formula of HfO_(x), where x may be within a range fromabout 1.70 to about 1.90, and the crystalline metal-rich oxide couplingmaterial has the generic chemical formula of ZrO_(y), where y may bewithin a range from about 1.70 to about 1.90. In other examples, x maybe within a range from about 1.75 to about 1.85 and y may be within arange from about 1.75 to about 1.85, for example, about 1.80. The metaloxide host layer may have a thickness within a range from about 5 Å toabout 100 Å, such as from about 10 Å to about 80 Å, such as from about15 Å to about 50 Å, for example, about 30 Å. The metal oxide couplinglayer may have a thickness within a range from about 3 Å to about 80 Å,such as from about 5 Å to about 20 Å, such as from about 5 Å to about 10Å , for example, about 8 Å.

In other examples, the crystalline metal-rich oxide host material hasthe generic chemical formula of HfO_(x), where x may be within a rangefrom about 1.70 to about 1.90, and the crystalline metal-rich oxidecoupling material has the generic chemical formula of HfO_(y) or TiO_(y)where y may be within a range from about 1.70 to about 1.90.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the inventioncan be understood in detail, a more particular description of theinvention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a flowchart illustrating a method to form a memory device, asdescribed by embodiments herein;

FIG. 2A depicts a memory device which may be formed by a methodillustrated in FIG. 1, as described by embodiments herein;

FIGS. 2B-2C depict various metal oxide film stacks which may be formedwithin the memory device illustrated in FIG. 2A, as described by otherembodiments herein; and

FIG. 3 depicts a memory array of resistive switching memory devices, asdescribed by another embodiment herein.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

Embodiments of the invention generally relate to nonvolatile memorydevices and methods for manufacturing such memory devices. Embodimentsof the invention generally relate to nonvolatile memory devices andmethods for manufacturing such memory devices. Embodiments describedherein provide methods for forming improved memory devices, such as aReRAM cells, and also provide optimized, atomic layer deposition (ALD)processes for forming metal oxide film stacks. The metal oxide filmstacks described herein contain at least two metal oxide layers adjacentto or in contact with each other, such as a metal oxide coupling layerdisposed on a metal oxide host layer. The metal oxide layers containdifferent metal oxide materials and each metal oxide material has adifferent grain structure and/or size from the other—therefore the metaloxide layers have a grain boundary disposed at the interfacetherebetween.

The interface disposed between the two metal oxide layers facilitatesoxygen vacancy movement or filamentary formation. The interface containsnumerous grain boundaries that extend parallel to the electrodeinterfaces, in contrast to the grains in the bulk film that extendperpendicular to the electrode interfaces. As a result, oxygen vacanciesare trapped and released during switching without any overall loss orwithout significant loss of vacancies. Therefore, the metal oxide filmstacks have improved switching performance and reliability during memorycell applications—compared to previous memory cells which generallycontain traditional hafnium oxide based stacks.

FIG. 1 is a flowchart illustrating a method for manufacturing orotherwise forming various memory devices, as described by embodimentsherein, such as process 100 which may be utilized to form resistiveswitching memory elements/devices, such as memory device 200, asdepicted in FIG. 2A. In one embodiment, process 100 may be used to formmemory device 200 and includes forming lower electrode 220 on or oversubstrate 210 during step 110, optionally forming silicon oxide layer222 on or over lower electrode 220 during step 120, forming metal oxidefilm stack 230 on or over silicon oxide layer 222 or lower electrode 220by ALD processes during step 130, optionally annealing memory device 200during step 135, depositing upper electrode 250 on or over metal oxidefilm stack 230 during step 140, and optionally annealing memory device200 during step 145. FIGS. 2B-2C depict a variety of metal oxide filmstacks 230 formed by different ALD techniques during step 130, asdescribed by embodiments herein.

In many embodiments, several different metal oxide film stacks 230, asdepicted in FIGS. 2B-2C, may be formed by different ALD techniquesduring step 130 of process 100, and contained within memory device 200depicted in FIG. 2A. Each of the metal oxide film stacks 230 depicted inFIGS. 2B-2C may be disposed between lower electrode 220 and upperelectrode 250 of memory device 200. Therefore, any of the particularlower layers depicted in each of the metal oxide film stacks 230 may beon or over lower electrode 220. Similarly, upper electrode 250 may be onor over any of the particular upper layers depicted in each of the metaloxide film stacks 230. Silicon oxide layer 222 may be deposited, formed,or otherwise disposed on or over lower electrode 220.

In one embodiment, a method for fabricating a resistive switching memoryelement, such as memory device 200, is provided and includes formingmetal oxide film stack 230 during step 130 of process 100. Metal oxidefilm stack 230 contains metal oxide coupling layer 234 disposed on metaloxide host layer 232, as depicted in FIG. 2B. Metal oxide host layer 232contains a crystalline metal-rich oxide host material and metal oxidecoupling layer 234 contains an amorphous metal-rich oxide couplingmaterial. Therefore, the crystalline structure of metal oxide host layer232 has a grain boundary at interface 233 which is adjacent to orotherwise in contact with the amorphous structure of metal oxidecoupling layer 234. Interface 233 facilitates oxygen vacancy between thecrystalline metal-rich oxide host material of metal oxide host layer 232and the amorphous metal-rich oxide coupling material of metal oxidecoupling layer 234. The crystalline metal-rich oxide host materialcontained within metal oxide host layer 232 may be represented by thegeneric chemical formula of MO_(x), where M is a metal selected fromhafnium, zirconium, or titanium and x may be within a range from about1.65 to about 1.95. The amorphous metal-rich oxide coupling materialcontained within metal oxide coupling layer 234 may be represented bythe generic chemical formula of MM′_(y)O_(z), where M is the same typeof metal selected for the crystalline metal-rich oxide host materialcontained within metal oxide host layer 232, M′ is a dopant metalselected from aluminum, yttrium, or lanthanum, y may be within a rangefrom about 0.05 to about 0.50, and z may be within a range from about1.50 to about 2.50.

In another embodiment, metal oxide film stack 230, formed during step130 of process 100, contains crystalline metal oxide coupling layer 244disposed on metal oxide host layer 232, as depicted in FIG. 2C. Metaloxide host layer 232 contains a crystalline metal-rich oxide hostmaterial and crystalline metal oxide coupling layer 244 contains acrystalline metal-rich oxide coupling material. The crystallinestructure of metal oxide host layer 232—having one grain boundary—isadjacent to or otherwise in contact with the crystalline structure ofcrystalline metal oxide coupling layer 244—having another grainboundary. The crystalline metal-rich oxide host material and thecrystalline metal-rich oxide coupling material have different averagegrain sizes relative to each other—therefore—have different grainboundaries at interface 243—which form a misaligned grain interface. Inmany examples, the average grain size of the crystalline metal-richoxide host material is greater than the average grain size of thecrystalline metal-rich oxide coupling material.

The misaligned grain interface facilitates oxygen vacancy between themetal-rich oxide host material contained within metal oxide host layer232 and the metal-rich oxide coupling material contained withincrystalline metal oxide coupling layer 244. The crystalline metal-richoxide host material of metal oxide host layer 232 may have the genericchemical formula of MO_(x), where M is a metal selected from hafnium,zirconium, or titanium and x may be within a range from about 1.65 toabout 1.95. The crystalline metal-rich oxide coupling material ofcrystalline metal oxide coupling layer 244 may have the generic chemicalformula of M′O_(y), where M′ is a metal selected from hafnium,zirconium, or titanium, y may be within a range from about 1.65 to about1.95.

In various embodiments, process 100 further provides step 120 whichincludes optionally forming silicon oxide layer 222 on or over lowerelectrode 220, and subsequently, forming metal oxide bulk layer 232 onor over silicon oxide layer 222, as depicted in FIGS. 2B-2C. Siliconoxide layer 222 contains a silicon oxide material, such as nativesilicon oxides, silicon dioxide, dopant variants thereof, orcombinations thereof. Silicon oxide layer 222 may contain a single layeror multiple layers of the same or different silicon oxide materials.Usually, silicon oxide layer 222 may be continuously formed, deposited,or otherwise disposed on or over lower electrode 220 or other underlyingsurfaces. Alternatively, silicon oxide layer 222 may also bediscontinuously formed, deposited, or otherwise disposed on or overlower electrode 220 or other underlying surfaces. Silicon oxide layer222 may have a thickness within a range from about 2 Å to about 40 Å,such as from about 2 Å to about 20 Å, such as from about 5 Å to about 10Å.

The method further provides forming metal oxide film stack 230 whichincludes depositing metal oxide host layer 232 over lower electrode 220during a first ALD process, wherein metal oxide host layer 232substantially contains a crystalline metal-rich oxide host material. Thecrystalline metal-rich oxide host material of metal oxide host layer 232may be represented by the generic chemical formula of MO_(x), where M isa metal selected from hafnium, zirconium, or titanium and x may bewithin a range from about 1.65 to about 1.95, such as from about 1.70 toabout 1.90, such as from about 1.75 to about 1.85, for example, about1.80. The method also includes depositing metal oxide coupling layer 234over metal oxide host layer 232 during a second ALD process, whereinmetal oxide coupling layer 234 is a metal oxide laminate andsubstantially contains an amorphous metal-rich oxide coupling material.

The amorphous metal-rich oxide coupling material of metal oxide couplinglayer 234 may be represented by the generic chemical formula ofMM'_(y)O_(z), where M is hafnium, zirconium, or titanium, M′ is a dopantmetal selected from aluminum, yttrium, or lanthanum, y may be within arange from about 0.05 to about 0.50, and z may be within a range fromabout 1.50 to about 2.50. In many embodiments, the amorphous metal-richoxide coupling material of metal oxide coupling layer 234 may berepresented by the generic chemical formula of MM′_(y)O_(z), where M isthe same type of metal as the metal selected for MO_(x), the crystallinemetal-rich oxide host material of metal oxide host layer 232. In analternative embodiment, the amorphous metal-rich oxide coupling material(MM′_(y)O_(z)) of metal oxide coupling layer 234 may contain a differentmetal M than the metal M selected for the crystalline metal-rich oxidehost material (MO_(x)) of metal oxide host layer 232.

The amorphous metal-rich oxide coupling material of metal oxide couplinglayer 234 may be lightly or heavily doped with aluminum, yttrium, orlanthanum, such as to have a dopant concentration may be provided by yand z values for MM′_(y)O_(z). In some of the light doping or lowconcentration examples, y may be within a range from about 0.05 to about0.15 and z may be within a range from about 1.50 to about 2.10. In someof the heavy doping or high concentration examples, y may be within arange from about 0.40 to about 0.50 and z may be within a range fromabout 2.10 to about 2.50.

In several examples described herein, metal oxide coupling layer 234contains an amorphous hafnium aluminate layer which may be deposited,formed, or otherwise disposed on or over metal oxide host layer 232containing a crystalline hafnium oxide layer. In one example, thecrystalline metal-rich oxide host material of metal oxide host layer 232may have the generic chemical formula of HfO_(x), where x may be withina range from about 1.65 to about 1.95, such as from about 1.70 to about1.90, such as from about 1.75 to about 1.85, for example, about 1.80.The amorphous hafnium aluminate of metal oxide coupling layer 234 mayhave the generic chemical formula of HfAl_(y)O_(z), where y may bewithin a range from about 0.05 to about 0.50, and z may be within arange from about 1.50 to about 2.50. Therefore, a light doping ofaluminum provides that y may be within a range from about 0.05 to about0.15 and z may be within a range from about 1.50 to about 2.10. A heavydoping of aluminum provides that y may be within a range from about 0.40to about 0.50 and z may be within a range from about 2.10 to about 2.50.

In one example, the amorphous metal-rich oxide coupling material ofmetal oxide coupling layer 234 contains hafnium aluminum oxide with ahigh aluminum doping concentration within a range from about 20 at %(atomic percent) to about 60 at %, such as from about 30 at % to about55 at %, such as from about 40 at % to about 50 at %, for example, about45 at % relative to the hafnium atomic concentration. In anotherexample, the amorphous metal-rich oxide coupling material of metal oxidecoupling layer 234 contains hafnium aluminum oxide with a low aluminumdoping concentration within a range from about 2 at % to about 20 at %,such as from about 4 at % to about 15 at %, such as from about 5 at % toabout 10 at %, for example, about 7 at % or about 8 at % relative to thehafnium atomic concentration.

Metal oxide host layer 232 may have a thickness within a range fromabout 5 Å to about 100 Å, such as from about 10 Å to about 80 Å, such asfrom about 15 Å to about 50 Å, for example, about 30 Å. Metal oxidecoupling layer 234 may have a thickness within a range from about 3 Å toabout 80 Å, such as from about 5 Å to about 50 Å, such as from about 5 Åto about 30 Å, for example, about 20 Å.

In one embodiment, the crystalline metal-rich oxide host material ofmetal oxide host layer 232 may be formed by a first ALD process whichincludes sequentially flowing, pulsing, or otherwise providing a metalsource gas and an oxidizing agent into a deposition chamber during ametal-rich oxidizing ALD process. The metal source gas may contain ahafnium precursor, a zirconium precursor, or a titanium precursor andthe oxidizing agent may contain water, ozone, oxygen plasma, or otheroxygen sources described herein. In some examples, the source gas maycontain a tetrakis(dialkylamido)hafnium compound, such astetrakis(dimethylamido)hafnium or a hafnium halide compound, such ashafnium tetrachloride, as the hafnium precursor and the oxidizing agentmay contain water during the metal-rich oxidizing ALD process.

Thereafter, the amorphous metal-rich oxide coupling material of metaloxide coupling layer 234 may be formed by a second ALD process whichincludes sequentially flowing, pulsing, or otherwise providing a firstmetal source gas, a second metal source gas, and an oxidizing agent intothe deposition chamber during a metal-rich oxidizing ALD process. Thefirst metal source gas may contain a hafnium precursor, a zirconiumprecursor, or a titanium precursor. In one embodiment, the first sourcegas is the same for both the first and second ALD processes. The secondmetal source may contain an aluminum precursor, an yttrium precursor, ora lanthanum precursor. The oxidizing agent may contain water, ozone,oxygen plasma, or other oxygen sources described herein. In someexamples, the first source gas may contain atetrakis(dialkylamido)hafnium compound, such astetrakis(dimethylamido)hafnium, the second metal source gas may containan alkyl aluminum compound, such as trimethylaluminum, and the oxidizingagent may contain water.

In another embodiment for forming metal oxide host layer 232, the firstALD process further includes sequentially flowing, pulsing, or otherwiseproviding a first metal source gas, a purge gas, an oxidizing agent, andthe purge gas into a deposition chamber while forming the crystallinemetal-rich oxide host material of during an ALD cycle of the first ALDprocess, and repeating the ALD cycle of the first ALD process whileincreasing the thickness of metal oxide host layer 232 until thethickness is within a range from about 5 Å to about 100 Å. Also, thesecond ALD process further includes sequentially flowing, pulsing, orotherwise providing a second metal source gas, the purge gas, the firstmetal source gas, the purge gas, the oxidizing agent, and the purge gasinto the deposition chamber while forming the amorphous metal-rich oxidecoupling material during an ALD cycle of the second ALD process.Thereafter, the method includes repeating the ALD cycle of the secondALD process while increasing the thickness of metal oxide coupling layer234 until the thickness is within a range from about 3 Å to about 80 Å.

In many of these examples, the first metal source gas may contain ahafnium precursor, such as tetrakis(dimethylamido)hafnium, the secondmetal source gas may contain an aluminum precursor, such astrimethylaluminum, the oxidizing agent may contain water, ozone, oroxygen plasma, and the purge gas may contain argon, nitrogen, hydrogen,mixtures thereof, or combinations thereof. In other examples, the firstmetal source gas may contain a zirconium precursor, such as atetrakis(dialkylamido)zirconium compound, for example,tetrakis(dimethylamido)zirconium, or a zirconium halide, such aszirconium tetrachloride. Also, the first metal source gas may contain atitanium precursor, such as a tetrakis(dialkylamido)titanium compound,for example, tetrakis(dimethylamido)titanium, or a titanium halide, suchas titanium tetrachloride.

In many embodiments, a grain size ratio of the average grain size of thecrystalline MO_(x) host material to the average grain size of thecrystalline M′O_(y) coupling material is greater than 1, such as withina range from about 1.05 to about 2.0 or greater. In some examples, thegrain size ratio may be within a range from about 1.10 to about 1.50,for example, about 1.25. The average grain size of the crystallineMO_(x) host material may be within a range from about 30 nm to about 40nm, and the average grain size of the crystalline MO_(x) couplingmaterial may be within a range from about 25 nm to about 35 nm.

The crystalline metal-rich oxide host material of metal oxide host layer232 may have the generic chemical formula of HfO_(x), where x may bewithin a range from about 1.70 to about 1.90, and the crystallinemetal-rich oxide coupling material of crystalline metal oxide couplinglayer 244 may have the generic chemical formula of ZrO_(y), where y maybe within a range from about 1.70 to about 1.90. In some examples, x maybe within a range from about 1.75 to about 1.85 and y may be within arange from about 1.75 to about 1.85, for example, about 1.80. Inadditional examples of the hafnium-rich oxide host material containedwithin metal oxide host layer 232, the crystalline metal-rich oxidecoupling material of crystalline metal oxide coupling layer 244 may havethe generic chemical formula of HfO_(y) or TiO_(y) where y may be withina range from about 1.70 to about 1.90.

Metal oxide host layer 232 may have a thickness within a range fromabout 5 Å to about 100 Å, such as from about 10 Å to about 80 Å, such asfrom about 15 Å to about 50 Å, for example, about 30 Å. Crystallinemetal oxide coupling layer 244 may have a thickness within a range fromabout 3 Å to about 80 Å, such as from about 5 Å to about 20 Å, such asfrom about 5 Å to about 10 Å, for example, about 8 Å.

In one embodiment, the first ALD process includes sequentially flowing,pulsing, or otherwise providing a metal source gas and an oxidizingagent into a deposition chamber during a metal-rich oxidizing ALDprocess while forming the crystalline metal-rich oxide host material ofmetal oxide host layer 232. The metal source gas may contain a hafniumprecursor, a zirconium precursor, or a titanium precursor and theoxidizing agent may contain water, ozone, oxygen plasma, or other oxygensources described herein. In some examples, atetrakis(dialkylamido)hafnium compound, such astetrakis(dimethylamido)hafnium, may be the hafnium precursor and theoxidizing agent may contain water during the metal-rich oxidizing ALDprocess.

The second ALD process includes sequentially flowing, pulsing, orotherwise providing a second metal source gas (e.g., zirconiumprecursor), and an oxidizing agent into the deposition chamber during ametal-rich oxidizing ALD process while forming the crystallinemetal-rich oxide coupling material of crystalline metal oxide couplinglayer 244. The oxidizing agent may be the same in the first and secondALD processes or a different oxidizing agent may be used in the secondALD process as used in the first ALD process.

The first metal source gas and the second metal source gas may eachindependently contain a hafnium precursor, a zirconium precursor, or atitanium precursor. Generally, the first metal source gas and the secondmetal source gas contain different metal precursors. In one example, thefirst metal source gas may contain a hafnium precursor and the secondmetal source gas may contain a zirconium precursor. The oxidizing agentmay contain water, ozone, oxygen plasma, or other oxygen sourcesdescribed herein. In some examples, the first source gas may contain atetrakis(dialkylamido)hafnium compound, such astetrakis(dimethylamido)hafnium or a hafnium halide compound, such ashafnium tetrachloride, the second metal source gas may contain atetrakis(dialkylamido)zirconium compound, such astetrakis(dimethylamido)zirconium or a zirconium halide compound, such aszirconium tetrachloride, and the oxidizing agent may contain water.

In another embodiment, the first ALD process further includessequentially flowing, pulsing, or otherwise providing a first metalsource gas, a purge gas, an oxidizing agent, and the purge gas into thedeposition chamber while forming the crystalline metal-rich oxide hostmaterial of metal oxide host layer 232 during an ALD cycle of the firstALD process, and repeating the ALD cycle of the first ALD process whileincreasing the thickness of metal oxide host layer 232 until thethickness is within a range from about 5 Å to about 100 Å.

Additionally, the second ALD process further includes sequentiallyflowing, pulsing, or otherwise providing a second metal source gas, thepurge gas, the oxidizing agent, and the purge gas into the depositionchamber while forming the crystalline metal-rich oxide coupling materialof crystalline metal oxide coupling layer 244 during an ALD cycle of thesecond ALD process. Thereafter, the method includes repeating the ALDcycle of the second ALD process while increasing the thickness ofcrystalline metal oxide coupling layer 244 until the thickness is withina range from about 3 Å to about 80 Å. The purge gas may contain argon,nitrogen, hydrogen, mixtures thereof, or combinations thereof.

In one embodiment described herein, substrate 210 and/or memory device200 may be maintained at a deposition temperature or a substratetemperature within a range from greater than 0° C. to about 20° C., suchas from greater than 0° C. to about 10° C., such as from greater than 0°C. to about 5° C., for example about 1° C. during the metal-richoxidizing ALD process.

Some of the materials and/or layers of metal oxide film stack 230 may bedeposited or otherwise formed using a variety of deposition techniques,but in many embodiments described herein, all of the materials and/orlayers of metal oxide film stack 230 may be deposited using thermal ALDprocesses and/or plasma-enhanced ALD (PE-ALD). In one embodiment, ametal-rich oxide material may be formed by a metal-rich oxidizing ALDprocess utilizing water and a metal-poor oxide material may be formed bya metal-poor oxidizing ALD process utilizing an activated oxygen agent,such as ozone, atomic oxygen, oxygen plasma, derivatives thereof, orcombinations thereof.

The ALD processes described herein may include heating the memorydevice, the substrate, or the substrate carrier/pedestal to a depositiontemperature within a range from about 50° C. to about 500° C., such asfrom about 200° C. to about 350° C., such as from about 250° C. to about300° C. In one example, the deposition temperature during a metal-pooroxidizing ALD process may be about 275° C. In another example, thedeposition temperature during a metal-rich oxidizing ALD process may beabout 250° C.

In one example, a method of process 100 for forming memory device 200 onthe surface of substrate 210 includes forming lower electrode 220containing polysilicon disposed on or over substrate 210 (step 110),optionally forming silicon oxide layer 222 on or over lower electrode220 (step 120), forming metal oxide film stack 230 on or over siliconoxide layer 222 and/or lower electrode 220 (step 130), optionallyannealing memory device 200 (step 135), depositing upper electrode 250on or over metal oxide film stack 230 (step 140), and optionallyannealing memory device 200 (step 145), such as a post electrode anneal.In many examples, lower electrode 220 contains an n-type polysiliconmaterial and upper electrode 250 contains titanium nitride or derivativethereof.

In another embodiment described herein, a method includes forming metaloxide film stack 230 during step 130 of process 100, wherein metal oxidehost layer 232 is treated to a first post metal oxide anneal and/or aplasma anneal prior to forming crystalline metal oxide coupling layer244. Subsequent the first post metal oxide anneal and/or a plasmaanneal, crystalline metal oxide coupling layer 244 may be formed on thetreated metal oxide host layer 232 while forming metal oxide film stack230, as depicted in FIG. 2C. Thereafter, metal oxide film stack 230containing crystalline metal oxide coupling layer 244 disposed on thetreated metal oxide host layer 232 may be exposed to a second post metaloxide anneal.

Step 130 includes the first post metal oxide anneal, the second postmetal oxide anneal, and/or the plasma anneal which each anneal processmay be done at various times within step 130. Interface 243 is amisaligned grain interface formed between the grain boundary of metaloxide host layer 232 and the grain boundary of crystalline metal oxidecoupling layer 244. The misaligned grain interface facilitates oxygenvacancy between the crystalline metal-rich oxide host material of metaloxide host layer 232 and the crystalline metal-rich oxide couplingmaterial of crystalline metal oxide coupling layer 244. Damage formed onthe upper surface of metal oxide host layer 232 by the plasma exposureforms a portion of interface 243. The plasma may be formed from a gascontaining argon, oxygen, ozone, an argon and oxygen mixture, orcombinations thereof.

In one example, metal oxide host layer 232 containing a hafnium-richoxide is deposited or otherwise formed on or over lower electrode 220 orsilicon oxide layer 222. Metal oxide host layer 232 may have a thicknesswithin a range from about 2 nm to about 3 nm. Thereafter, metal oxidehost layer 232 is exposed to a first post metal oxide anneal at atemperature of about 750° C. for about 1 minute, then exposed to anargon plasma treatment for about 30 seconds. Crystalline metal oxidecoupling layer 244 is deposited or otherwise formed on the treated metaloxide host layer 232. Crystalline metal oxide coupling layer 244 mayhave a thickness of about 1 nm. Thereafter, crystalline metal oxidecoupling layer 244 is exposed to a second post metal oxide anneal at atemperature within a range from about 600° C. to about 750° C. for about1 minute.

Memory device 200 containing metal oxide film stack 230, or a portion ofmetal oxide film stack 230, may optionally be exposed to a firstannealing process, such as a post metal oxide anneal, during step 135 ofprocess 100. In one embodiment, the post metal oxide anneal issubsequent to depositing or forming metal oxide host layer 232, butprior to forming amorphous metal oxide coupling layer 234 or crystallinemetal oxide coupling layer 244. Alternatively, the post metal oxideanneal may be subsequent to forming amorphous metal oxide coupling layer234 or crystalline metal oxide coupling layer 244. During the post metaloxide anneal, metal oxide film stack 230, metal oxide host layer 232,amorphous metal oxide coupling layer 234, and/or, crystalline metaloxide coupling layer 244 may be heated to an annealing temperaturewithin a range from about 250° C. to about 800° C., such as from about400° C. to about 700° C., or from about 500° C. to about 600° C., forexample, about 550° C. Generally, memory device 200 containing any ofthe layers or films of metal oxide film stack 230 may be heated for atime period within a range from about 30 seconds to about 10 minutes,such as from about 1 minute to about 8 minutes, or from about 4 minutesto about 6 minutes during the post metal oxide anneal of step 135.

The post metal oxide anneal may be conducted within an annealingchamber, vacuum chamber, deposition chamber, or other processing chamberthat provides heat to the layers contained within metal oxide film stack230. In some examples, metal oxide film stack 230, metal oxide hostlayer 232, amorphous metal oxide coupling layer 234, and/or, crystallinemetal oxide coupling layer 244 may be heated to an annealing temperaturewithin a range from about 475° C. to about 625° C. for a time periodwithin a range from about 3 minutes to about 7 minutes during the postmetal oxide anneal at step 135. In one example, the annealingtemperature of about 550° C. for about 5 minutes is used during the postmetal oxide anneal.

FIG. 2A depicts memory device 200 containing metal oxide film stack 230disposed between at least two electrodes, such as lower electrode 220and upper electrode 250, and lower electrode 220 is disposed orotherwise supported on substrate 210. Substrate 210 supports lowerelectrode 220 while depositing and forming each of the layers withinmemory device 200—and for subsequent manufacturing processes. Substrate210 may be wafer or other substrate and contain silicon, doped silicon,Group III-V materials (e.g., GaAs), or derivates thereof. In mostexamples described herein, substrate 210 is a crystalline silicon waferthat may be doped with a dopant element. Lower electrode 220 may containa doped silicon material, for example p-type or n-type (N+) dopedpolysilicon. Lower electrode 220 may be deposited or otherwise formed onor over substrate 210 during step 110.

Lower electrode 220 and upper electrode 250 may independently contain orbe formed of one material or multiple materials and generally contain orformed of different conductive materials relative to each other.Numerous exemplary electrode materials that may be useful for lowerelectrode 220 and upper electrode 250 are provided in the writtendescription herein. These electrode materials are only exemplary andshould not be limited in scope relative to the variety of materials thatmay be independently contained within lower electrode 220 and upperelectrode 250. In some embodiments, lower electrode 220 and upperelectrode 250 have work functions that differ by an energy level withina range from about 0.1 eV to about 1 eV, such as, from about 0.4 eV toabout 0.6 eV. In some examples, lower electrode 220 may contain a n-typepolysilicon material which has a work function within a range from about4.1 eV to about 4.15 eV and upper electrode 250 may contain a titaniumnitride material which has a work function within a range from about 4.5eV to about 4.6 eV. Other exemplary electrode materials that may becontained within lower electrode 220 and/or upper electrode 250 includep-type polysilicon (about 4.9 eV to about 5.3 eV), transition metals,transition metal alloys, transition metal nitrides, transition metalcarbides, tungsten (about 4.5 eV to about 4.6 eV), tantalum nitride(about 4.7 eV to about 4.8 eV), molybdenum oxide (about 5.1 eV),molybdenum nitride (about 4.0 eV to about 5.0 eV), iridium (about 4.6 eVto about 5.3 eV), iridium oxide (about 4.2 eV), ruthenium (about 4.7eV), and ruthenium oxide (about 5.0 eV). Other exemplary electrodematerials for lower electrode 220 and/or upper electrode 250 include atitanium/aluminum alloy (about 4.1 eV to about 4.3 eV), nickel (about5.0 eV), tungsten nitride (about 4.3 eV to about 5.0 eV), tungsten oxide(about 5.5 eV to about 5.7 eV), aluminum (about 4.2 eV to about 4.3 eV),copper or silicon-doped aluminum (about 4.1 eV to about 4.4 eV), copper(about 4.5 eV), hafnium carbide (about 4.8 eV to about 4.9 eV), hafniumnitride (about 4.7 eV to about 4.8 eV), niobium nitride (about 4.95 eV),tantalum carbide (about 5.1 eV), tantalum silicon nitride (about 4.4eV), titanium (about 4.1 eV to about 4.4 eV), vanadium carbide (about5.15 eV), vanadium nitride (about 5.15 eV), and zirconium nitride (about4.6 eV). For some embodiments described herein, the higher work functionelectrode receives a positive pulse (as measured compared to a commonreference potential) during a reset operation, although other materialsand configurations are possible.

In other embodiments, the higher work function electrode receives anegative pulse during a reset operation. In some examples, upperelectrode 250 may contain metals, metal carbides, metal oxides, or metalnitrides, which include, for example, platinum, palladium, ruthenium,ruthenium oxide, iridium, iridium oxide, titanium, titanium nitride,tungsten, tungsten oxide, tungsten nitride, tungsten carbide, tantalum,tantalum oxide, tantalum nitride, tantalum silicon nitride, tantalumcarbide, molybdenum, molybdenum oxide, molybdenum nitride, titaniumaluminum alloys, nickel, aluminum, doped aluminum, aluminum oxide,copper, hafnium carbide, hafnium nitride, niobium nitride, vanadiumcarbide, vanadium nitride, zirconium nitride, derivatives thereof, orcombinations thereof. In many examples, upper electrode 250 containstitanium, titanium nitride, alloys thereof, or combinations thereof.

Memory device 200 containing upper electrode 250 deposited, formed, orotherwise disposed on or over metal oxide film stack 230 may optionallybe exposed to a second annealing process, such as a post electrodeanneal, during step 145 of process 100. The post electrode anneal occurssubsequent to the formation of upper electrode 250. During the postelectrode anneal, memory device 200, including upper electrode 250 andmetal oxide film stack 230, may be heated to an annealing temperaturewithin a range from about 400° C. to about 1,200° C., such as from about500° C. to about 900° C., or from about 700° C. to about 800° C., forexample, about 750° C. Generally, memory device 200 may be heated for atime period within a range from about 10 seconds to about 5 minutes,such as from about 20 seconds to about 4 minutes, or from about 40seconds to about 2 minutes during the post upper electrode anneal ofstep 145. The post electrode anneal may be conducted within an annealingchamber, vacuum chamber, deposition chamber, or other processing chamberthat provides heat to the layers contained within memory device 200,such as metal oxide film stack 230 and upper electrode 250.

In some examples, memory device 200 containing upper electrode 250 maybe heated to an annealing temperature within a range from about 700° C.to about 800° C. for a time period within a range from about 40 secondsto about 2 minutes during the post upper electrode anneal at step 145.In one example, the annealing temperature of about 750° C. for about 1minute is used during the annealing process.

FIG. 3 depicts a memory array 300 of resistive switching memory devices310, as described by embodiments herein. Each memory device 310 containsat least one switching memory element 312, and may contain multipleswitching memory elements 312. In some embodiments, memory devices 310may be a plurality of memory devices 200, depicted in FIG. 2A. Eachmemory device 200 may independently contain any of the metal oxide filmstacks 230 illustrated in FIGS. 2B-2C. Memory array 300 may be part of alarger memory device or other integrated circuit structure, such as asystem on a chip type device. Read and write circuitry is connected toswitching memory devices 310 using electrodes 322 and electrodes 324.Electrodes, such as upper electrodes 322 and lower electrodes 324, aresometimes referred to as word lines and bit lines, and are used to readand write data into the memory elements 312 in the switching memorydevices 310. Individual switching memory devices 310 or groups ofswitching memory devices 310 can be addressed using appropriate sets ofelectrodes 322 and 324. The memory elements 312 in the switching memorydevices 310 may be formed from a plurality of layers 314 a, 314 b, 314c, and 314 d containing various materials, as indicated schematically inFIG. 3. In addition, memory arrays such as memory array 300 can bestacked in a vertical fashion to make multilayer memory arraystructures.

According to various embodiments, resistive-switching memoryelements/devices are described herein. The memory elements/devicesgenerally have a structure in which resistive-switching insulatinglayers are surrounded by two conductive electrodes. Some embodimentsdescribed herein are memory elements that include electrodes ofdifferent materials (e.g., one electrode is doped silicon and one istitanium nitride) surrounding a resistive-switching layer of a metaloxide (e.g., hafnium oxide), thickness (about 20 Å to about 100 Å) and acoupling layer that is substantially thinner than theresistive-switching layer (e.g., less than 25% the thickness of theresistive-switching layer). In some embodiments, the coupling layer maybe a metallic material such as titanium. Memory elements including thecoupling layer have exhibited improved switching characteristics (e.g.,lower set, reset, and forming voltages, and better retention). In someembodiments, the resistive-switching layer includes a higher bandgapmaterial (e.g., a material having a bandgap greater than 4 eV such ashafnium oxide, aluminum oxide, tantalum oxide, yttrium oxide, zirconiumoxide, cerium oxide, alloys thereof, derivatives thereof, orcombinations thereof), however other resistive-switching layers mayinclude materials having a bandgap less than 4 eV (e.g., titaniumoxide).

ALD Processes

The exemplary ALD processes for depositing or otherwise forming themetal oxide materials contained within metal oxide film stack 230 andother materials and/or layers contained within memory device 200 aretypically conducted in a deposition chamber, such as an ALD chamber. Thedeposition chamber may maintain an internal pressure of less than 760Torr, such as within the range from about 10 mTorr to about 10 Torr,such as from about 100 mTorr to about 1 Torr, for example, about 350mTorr. The temperature of the memory device, the substrate, or thesubstrate carrier/pedestal is usually maintained within the range fromabout 50° C. to about 1,000° C., such as from about 100° C. to about500° C., such as from about 200° C. to about 400° C., or such as fromabout 250° C. to about 300° C.

The metal source gas may be pulsed, introduced, or otherwise providedinto the deposition chamber at a flow rate within the range from about0.1 sccm to about 200 sccm, such as from about 0.5 sccm to about 50sccm, from about 1 sccm to about 30 sccm, for example, about 10 sccm.The metal source gas may be provided along with a carrier gas, such asargon or nitrogen. The carrier gas may have a flow rate within the rangefrom about 1 sccm to about 300 sccm, such as from about 2 sccm to about80 sccm, from about 5 sccm to about 40 sccm, for example, about 20 sccm.

The metal source gas may be pulsed or otherwise provided into thedeposition chamber at a rate within a range from about 0.01 seconds toabout 10 seconds, depending on the particular process conditions, metalsource gas or desired composition of the deposited metal oxide material.In one embodiment, such as for forming a metal-poor oxide material, themetal source gas may be pulsed, introduced, or otherwise provided intothe deposition chamber at a rate within a range from about 1 second toabout 10 seconds, such as from about 1 second to about 5 seconds, forexample, about 3 seconds. In another embodiment, such as for forming ametal-rich oxide material, the metal source gas may be pulsed,introduced, or otherwise provided into the deposition chamber at a ratewithin a range from about 0.05 seconds to about 2 seconds, such as fromabout 0.1 seconds to about 1 second, for example, about 0.5 seconds. Inmany examples, the metal source gas is a hafnium precursor which is atetrakis(dialkylamino)hafnium compound, such astetrakis(dimethylamino)hafnium ((Me₂N)₄Hf or TDMAH),tetrakis(diethylamino)hafnium ((Et₂N)₄Hf or TDEAH), ortetrakis(ethylmethylamino)hafnium ((EtMeN)₄Hf or TEMAH).

The metal source gas is generally dispensed into a deposition chamber byintroducing a carrier gas through an ampoule containing the metal sourceor precursor. An ampoule unit may include an ampoule, a bubbler, acanister, a cartridge, or other container used for storing, containing,or dispersing chemical precursors. In another example, the ampoule maycontain a liquid precursor (e.g., TDMAH or TDEAH) and be part of aliquid delivery system containing injector valve system used to vaporizethe liquid precursor with a heated carrier gas. Generally, the ampoulemay be heated to a temperature of about 100° C. or less, such as withina range from about 30° C. to about 90° C., for example, about 50° C.

The oxidizing agent (e.g., O₂, O₃, H₂O) may be pulsed, introduced, orotherwise provided into the deposition chamber at a flow rate within arange from about 0.01 seconds to about 10 seconds, depending on theparticular process conditions, oxygen source gas or oxidizing agent ordesired composition of the deposited metal oxide material. In oneembodiment, such as for forming a metal-poor oxide material, theoxidizing agent may be pulsed, introduced, or otherwise provided intothe deposition chamber at a rate within a range from about 0.001 secondsto about 1 second, such as from about 0.001 seconds to about 0.1seconds, for example, about 0.05 seconds. In another embodiment, such asfor forming a metal-rich oxide material, the oxidizing agent may bepulsed, introduced, or otherwise provided into the deposition chamber ata rate within a range from about 0.5 second to about 10 seconds, such asfrom about 1 second to about 3 seconds, for example, about 2 seconds.

The oxidizing agent may contain or be formed of or generated from anoxygen source that includes oxygen (O₂), atomic oxygen (O), ozone (O₃),nitrous oxide (N₂O), nitric oxide (NO), nitrogen dioxide (NO₂),dinitrogen pentoxide (N₂O₅), hydrogen peroxide (H₂O₂), derivativesthereof, plasmas thereof, or combinations thereof. Ozone may be formedinside or outside of the deposition chamber, such as the ALD chamber. Inone example, the oxidizing agent contains ozone formed by an ozonegenerator positioned outside of the interior of the deposition chamber.Ozone is generated and then flowed or directed into the depositionchamber and exposed along with the metal source gas to the substratesurface. In another example, the oxidizing agent contains ozone formedby a plasma generated within the interior of the deposition chamber.Oxygen gas flowed or directed into the deposition chamber, then ignitedor formed into ozone and/or atomic oxygen before being sequentiallyexposed along with the metal source gas to the substrate surface.

A carrier gas or a purge gas may be provided at the same time as themetal source gas and/or the oxygen source, but is also provided betweenthe pulses of the metal source gas and/or the oxygen source. The carriergas or purge gas may continuous flow during the ALD process or may beintermediately and/or sequentially pulsed, introduced, or otherwiseprovided during the ALD. The carrier gas or purge gas may be pulsed,introduced, or otherwise provided into the deposition chamber at a ratewithin a range from about 1 second to about 30 seconds, depending on theparticular process conditions, source gases, or desired composition ofthe deposited metal oxide material. In one embodiment, the carrier gasor a purge gas may be pulsed, introduced, or otherwise provided into thedeposition chamber at a rate within a range from about 1 second to about30 seconds, such as from about 2 seconds to about 20 seconds, forexample, about 10 seconds or about 15 seconds.

The carrier gas or purge gas may contain nitrogen, argon, helium,hydrogen, a forming gas, oxygen, mixtures thereof, or combinationsthereof. The carrier gas or the purge gas may be sequentially pulsed,introduced, or otherwise provided after each pulse of the metal sourcegas and each pulse of the oxidizing agent during the ALD cycle. Thepulses of purge gas or carrier gas are typically pulsed, introduced, orotherwise provided at a flow rate within a range from about 2 standardliters per minute (slm) to about 22 slm, such as about 10 slm. Thespecific purge gas flow rates and duration of process cycles areobtained through experimentation. In one example, a 300 mm diameterwafer requires about twice the flow rate for the same duration as a 200mm diameter wafer in order to maintain similar throughput.

Many precursors are within the scope of embodiments of the invention fordepositing the dielectric materials described herein. One importantprecursor property is to have a favorable vapor pressure. Precursors atambient temperature and pressure may be gas, liquid, or solid. However,volatilized precursors are used within the ALD chamber. Organic-metalliccompounds contain at least one metal atom and at least oneorganic-containing functional group, such as amides, alkyls, alkoxyls,alkylaminos, anilides, or derivatives thereof. Precursors may includeorganic-metallic, organometallic, inorganic, or halide compounds.

In one embodiment, the metal source gas is formed from or contains atetrakis(dialkylamino)metal compound, such as atetrakis(dialkylamino)hafnium compound, atetrakis(dialkylamino)zirconium compound, or atetrakis(dialkylamino)titanium compound. Tetrakis(dialkylamino)metalcompounds are useful for depositing metal oxides contained within metaloxide film stack 230 and other materials and/or layers within memorydevice 200 during ALD processes.

In some examples, the metal source gas contains or is formed fromexemplary hafnium precursors which include hafnium compounds containingligands such as halides, alkylaminos, cyclopentadienyls, alkyls,alkoxides, derivatives thereof, or combinations thereof. Hafniumalkylamino compounds useful as hafnium precursors includetetrakis(dialkylamino)hafnium compounds, such as (RR′N)₄Hf, where R orR′ are independently hydrogen, methyl, ethyl, propyl, or butyl. Hafniumhalide compounds useful as hafnium precursors may include HfCl₄, Hfl₄,and HfBr₄. Exemplary hafnium precursors useful for depositing hafniumoxides and other hafnium-containing materials contained within metaloxide film stack 230 and other materials and/or layers within memorydevice 200 during ALD processes include (Et₂N)₄Hf, (Me₂N)₄Hf,(MeEtN)₄Hf, (^(t)BuC₅H₄)₂HfCl₂, (C₅H₅)₂HfCl₂, (EtC₅H₄)₂HfCl₂,(Me₅C₅)₂HfCl₂, (Me₅C₅)HfCl₃, (^(i)PrC₅H₄)₂HfCl₂, (^(i)PrC₅H₄)HfCl₃,(^(t)BuC₅H₄)₂HfMe₂, (acac)₄Hf, (hfac)₄Hf, (tfac)₄Hf, (thd)₄Hf, (NO₃)₄Hf,(^(t)BuO)₄Hf, (^(i)PrO)₄Hf, (EtO)₄Hf, (MeO)₄Hf, or derivatives thereof.

In other examples, the metal source gas contains or is formed fromexemplary zirconium precursors which include zirconium compoundscontaining ligands such as halides, alkylaminos, cyclopentadienyls,alkyls, alkoxides, derivatives thereof, or combinations thereof.Zirconium alkylamino compounds useful as zirconium precursors includetetrakis(dialkylamino) zirconium compounds, such as (RR′N)₄Zr, where Ror R′ are independently hydrogen, methyl, ethyl, propyl, or butyl.Zirconium halide compounds useful as zirconium precursors may includeZrCl₄, ZrCl₄, and ZrBr₄. Exemplary zirconium precursors useful fordepositing zirconium oxides and other zirconium-containing materialscontained within metal oxide film stack 230 and other materials and/orlayers within memory device 200 during ALD processes include (Et₂N)₄Zr,(Me₂N)₄Zr, (MeEtN)₄Zr, (^(t)BuC₅H₄)₂ZrCl₂, (C₅H₅)₂ZrCl₂, (EtC₅H₄)₂ZrCl₂,(Me₅C₅)₂ZrCl₂, (Me₅C₅)ZrCl₃, (^(t)PrC₅H₄)₂ZrCl₂, (^(i)PrC₅H₄)ZrCl₃,(^(t)BuC₅H₄)₂ZrMe₂, (acac)₄Zr, (hfac)₄Zr, (tfac)₄Zr, (thd)₄Zr, (NO₃)₄Zr,(^(t)BuO)₄Zr, (^(i)PrO)₄Zr, (EtO)₄Zr, (MeO)₄Zr, or derivatives thereof.

In other examples, the metal source gas contains or is formed fromexemplary titanium precursors which include titanium compoundscontaining ligands such as halides, alkylaminos, cyclopentadienyls,alkyls, alkoxides, derivatives thereof, or combinations thereof.Titanium alkylamino compounds useful as titanium precursors includetetrakis(dialkylamino)titanium compounds, such as (RR′N)₄Ti, where R orR′ are independently hydrogen, methyl, ethyl, propyl, or butyl. Titaniumhalide compounds useful as titanium precursors may include TiCl₄, TiI₄,and TiBr₄. Exemplary titanium precursors useful for depositing titaniumoxides and other titanium-containing materials contained within metaloxide film stack 230 and other materials and/or layers within memorydevice 200 during ALD processes include (Et₂N)₄Ti, (Me₂N)₄Ti,(MeEtN)₄Ti, (BuC₅H₄)₂TiCl₂, (C₅H₅)₂TiCl₂, (EtC₅H₄)₂TiCl₂, (Me₅C₅)₂TiCl₂,(Me₅C₅)TiCl₃, (^(i)PrC₅H₄)₂TiCl₂, (^(i)PrC₅H₄)TiCl₃, (BuC₅H₄)₂TiMe₂,(acac)₄Ti, (hfac)₄Ti, (tfac)₄Ti, (thd)₄Ti, (NO₃)₄Ti, (^(t)BuO)₄Ti,(^(i)PrO)₄Ti, (EtO)₄Ti, (MeO)₄Ti, or derivatives thereof.

In other examples, the metal source gas contains or is formed fromexemplary aluminum precursors which include aluminum compoundscontaining ligands such as halides, alkyls, alkoxides, derivativesthereof, or combinations thereof. Alkyl aluminum compounds useful asaluminum precursors may have the generic chemical formula of RR′R″Al,where each R, R′, and R″ may independently be hydrogen, methyl, ethyl,propyl, or butyl. Aluminum alkoxide compounds useful as aluminumprecursors may have the generic chemical formula of (RO)(R′O)(R″O)Al,where each R, R′, and R″ may independently be hydrogen, methyl, ethyl,propyl, or butyl. Aluminum halide compounds useful as aluminumprecursors may include AlCl₃, or AlF₃. Exemplary aluminum precursorsuseful for depositing aluminum oxides and other aluminum-containingmaterials contained within metal oxide film stack 230, metal oxidecoupling layer 234, and other materials and/or layers within memorydevice 200 during ALD processes include Me₃Al, Me₂AlH, Et₃Al, Et₂AlH,Pr₃Al, Pr₂AlH, Bu₃Al, Bu₂AlH, (^(t)BuO)₃Al, (^(i)PrO)₃Al, (EtO)₃Al,(MeO)₃Al, or derivatives thereof.

The ALD processes, as disclosed herein by the written description, areprovided as exemplary ALD processes and should not be limited in scoperelative to the variety of ALD processes that may be useful fordepositing or otherwise forming the metal oxide materials containedwithin metal oxide film stack 230 and other materials and/or layerscontained within memory device 200. Chemical precursors, carrier gases,pulse times, exposure times, flow rates, temperatures, pressures,sequence orders, and other variables may be adjusted accordingly inorder to form the desired thickness and stoichiometry of the metal oxidematerials contained within metal oxide film stack 230 and othermaterials and/or layers contained within memory device 200.

“ALD” as used herein refers to the sequential introduction of two ormore reactive compounds to deposit a layer of material on a substratesurface. The two, three or more reactive compounds may alternatively beintroduced into a reaction zone of a deposition chamber. Usually, eachreactive compound is separated by a time delay to allow each compound toadhere and/or react on the substrate surface. In one aspect, a firstprecursor or compound A is pulsed into the reaction zone of a depositionchamber (e.g., ALD chamber) followed by a first time delay. Next, asecond precursor or compound B is pulsed into the reaction zone followedby a second delay. During each time delay a purge gas, such as argon ornitrogen, may be pulsed or otherwise provided into the depositionchamber to purge the reaction zone or otherwise remove any residualreactive compound or by-products from the reaction zone or othersurfaces. Alternatively, the purge gas may flow continuously throughoutthe deposition process so that only the purge gas flows during the timedelay between pulses of reactive compounds. The reactive compounds arealternatively pulsed until a desired film or film thickness is formed onthe substrate or deposition. In either scenario of a continuous orintermittent purge gas flow, the ALD process of pulsing compound A,purge gas, pulsing compound B, and purge gas is an ALD cycle. An ALDcycle can start with either compound A or compound B and continue therespective order of the ALD cycle until achieving a film with thedesired thickness. In another aspect, a first precursor or compound A ispulsed into the reaction zone of a deposition chamber (e.g., ALDchamber) followed by a first time delay. Next, a second precursor orcompound B is pulsed into the reaction zone followed by a second delay.Next, a third precursor or compound C is pulsed into the reaction zonefollowed by a third delay. During each time delay a purge gas, such asargon or nitrogen, may be pulsed or otherwise provided into thedeposition chamber to purge the reaction zone or otherwise remove anyresidual reactive compound or by-products from the reaction zone orother surfaces. Alternatively, the purge gas may flow continuouslythroughout the deposition process so that only the purge gas flowsduring the time delay between pulses of reactive compounds. The reactivecompounds are alternatively pulsed until a desired film or filmthickness is formed on the substrate or deposition surface. In eitherscenario of a continuous or intermittent purge gas flow, the ALD processof pulsing compound A, purge gas, pulsing compound B, purge gas, pulsingcompound C, and purge gas is an ALD cycle. Alternatively, the ALDprocess of pulsing compound A, purge gas, pulsing compound B, purge gas,pulsing compound C, purge gas, pulsing compound B, and purge gas is anALD cycle. An ALD cycle can start with either compound A, compound B, orcompound C and continue the respective order of the ALD cycle untilachieving a film with the desired thickness.

A “pulse” as used herein is intended to refer to a quantity of aparticular compound that is intermittently or non-continuouslyintroduced into a reaction zone of a processing chamber. The quantity ofa particular compound within each pulse may vary over time, depending onthe duration of the pulse. The duration of each pulse is variabledepending upon a number of factors such as, for example, the volumecapacity of the deposition chamber employed, the vacuum system coupledthereto, and the volatility/reactivity of the particular compounditself. A “half-reaction” as used herein is intended to refer to a pulseof precursor step followed by a purge step.

While the foregoing is directed to embodiments of the invention, otherand further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A resistive random access memory cell comprising: a first electrode;a second electrode; a coupling layer comprising a first metal oxide, thecoupling layer being disposed between the first electrode and the secondelectrode, the coupling layer forming a first interface with the firstelectrode; and a host layer comprising a second metal oxide, the hostlayer being disposed between the first electrode and the secondelectrode, the host layer forming a second interface with the secondelectrode, wherein at least one of the coupling layer or the host layeris crystalline and forms a grain boundary interface with a remaining oneof the coupling layer or the host layer, the grain boundary interfacecomprising grain boundaries extending parallel to the first interfaceand the second interface.
 2. The resistive random access memory cell ofclaim 1, wherein the coupling layer is amorphous
 3. The resistive randomaccess memory cell of claim 2, wherein the host layer is crystalline 4.The resistive random access memory cell of claim 1, wherein the couplinglayer and the host layer are crystalline, and wherein the coupling layerand the host layer differ in at least one of a grain structure or agrain size thereby forming a misaligned grain interface between thecoupling layer and the host layer.
 5. The resistive random access memorycell of claim 4, wherein the grain size of the host layer is greater onaverage than the grain the grain size of the coupling layer.
 6. Theresistive random access memory cell of claim 1, wherein the second metaloxide has a generic chemical formula of MO_(x), where M is one ofhafnium, zirconium, or titanium and x is within a range from about 1.65to about 1.95.
 7. The resistive random access memory cell of claim 1,wherein the second metal oxide has a generic chemical formula ofHfO_(x), where x is within a range from about 1.70 to about 1.90.
 8. Theresistive random access memory cell of claim 1, wherein the second metaloxide has a generic chemical formula of HfO_(x), where x is within arange from about 1.75 to about 1.85.
 9. The resistive random accessmemory cell of claim 1, wherein the first metal oxide has a genericchemical formula of MM′_(y)O_(z), where M is the same type of metalselected for the first metal oxide host material, M′ is one of aluminum,yttrium, and lanthanum, y is within a range from about 0.05 to about0.50, and z is within a range from about 1.50 to about 2.50.
 10. Theresistive random access memory cell of claim 1, wherein the first metaloxide has a generic chemical formula of HfAl_(y)O_(z), where y is withina range from about 0.05 to about 0.50, and z is within a range fromabout 1.50 to about 2.50.
 11. The resistive random access memory cell ofclaim 1, wherein the first metal oxide has a generic chemical formula ofHfAl_(y)O_(z), where y is within a range from about 0.05 to about 0.15and z is within a range from about 1.50 to about 2.10.
 12. The resistiverandom access memory cell of claim 1, wherein the first metal oxide hasa generic chemical formula of HfAl_(y)O_(z), where y is within a rangefrom about 0.40 to about 0.50 and z is within a range from about 2.10 toabout 2.50.
 13. The resistive random access memory cell of claim 1,wherein the host layer has a thickness within a range from about 5 Å toabout 100 Å.
 14. The resistive random access memory cell of claim 1,wherein the host layer has a thickness within a range from about 10 Å toabout 80 Å.
 15. The resistive random access memory cell of claim 1,wherein the host layer has a thickness within a range from about 15 Å toabout 50 Å.
 16. The resistive random access memory cell of claim 1,wherein the coupling layer has a thickness within a range from about 3 Åto about 80 Å.
 17. The resistive random access memory cell of claim 1,wherein the coupling layer has a thickness within a range from about 5 Åto about 50 Å.
 18. The resistive random access memory cell of claim 1,wherein the coupling layer has a thickness within a range from about 5 Åto about 30 Å.
 19. The resistive random access memory cell of claim 1,further comprising a layer comprising silicon oxide, the layer beingdisposed between the first electrode and the coupling layer.
 20. Aresistive random access memory cell comprising: a first electrodecomprising titanium nitride; a second electrode comprising an n-typepolysilicon; a coupling layer comprising a first metal oxide having ageneric chemical formula of HfAl_(y)O_(z), where y is within a rangefrom about 0.05 to about 0.15 and z is within a range from about 1.50 toabout 2.10, the coupling layer having a thickness within a range fromabout 5 Å to about 30 Å, the coupling layer being disposed between thefirst electrode and the second electrode, the coupling layer forming afirst interface with the first electrode; and a host layer comprising asecond metal oxide having a generic chemical formula of HfO_(x), where xis within a range from about 1.75 to about 1.85, the host layer having athickness within a range from about 15 Å to about 50 Å, the host layerbeing disposed between the first electrode and the second electrode, thehost layer forming a second interface with the second electrode, whereinthe host layer forms a grain boundary interface with the coupling layer,the grain boundary interface comprising grain boundaries extendingparallel to the first interface and the second interface.